[musicale]

Good idea. I'd much rather write

   do concurrent (i = 1:n) 
     y(i) = y(i) + a*x(i)
   enddo

and then let the a compiler translate it into

    std::transform(par, x, x+n, y, y,
      [=](float x, float y){ return y + a*x; }
    );

if C++ is required for some reason.